Longitudinal measurement invariance of the Psychotic-Like Experiences Questionnaire for Children (PLEQ-C).

Psychotic-Like Experiences (PLEs) are subclinical perceptions, thoughts, or beliefs that, while considered unusual, are commonly self-reported during childhood. Though typically transient, childhood PLEs may index an increased risk for psychosis (and other psychiatric disorders), particularly when they persist over time. Brief self-report questionnaires provide a feasible means of population screening for PLEs and their persistence; however, there is limited evidence to confirm the longitudinal stability of self-report PLE measurement among children. The aim of the present study was to investigate the longitudinal measurement invariance of the nine-item self-report Psychotic-Like Experiences Questionnaire for Children (PLEQ-C) in a community sample of 9-to-12-year-old children (n = 270) for whom baseline and follow-up data were available. Longitudinal invariance testing was conducted using multi-group confirmatory analyses on data from three gender-balanced groups of 90 children, each with equivalent baseline age (mean = 10.3 years), but variable follow-up periods of 12 months (mean age = 11.3 years), 24 months (mean age = 12.2 years), and 36 months (mean age = 13.4 years), respectively. Full configural, metric, scalar, and residual invariance of the PLEQ-C was demonstrated across all three follow-up periods, indicating that items were consistently interpreted by children into early adolescence. Findings endorse the use of an age-appropriate measure developed for children - the PLEQ-C - as a robust self-report tool that can reliably screen and monitor PLEs in the general population over a three-year period from the age of 10 years, and identify children who might benefit from further (clinical) investigation.